Percentages of iron oxide

We have access to 99% iron oxide through our closest supplier, however we find that 84% works better to get the best contrasts in our Temoku glaze. When looking at glaze formulas in texts and journals the percent content is usually not highlighted. We have found that Spanish RIO is not a direct substitution. I am just asking for clarification which iron is the best choice for trying out new glaze recipes.
Thank you for any information about this question.
V

I have been using spanish for many years now-before that The domestic was all I ever saw.I also have used High Purity from US Pigments as well.Back in the day Domestic was all that I recall was around.So we always used that in all recipes.Now its spanish or High Purity for me.Mark

I have been using spanish for many years now-before that The domestic was all I ever saw.I also have used High Purity from US Pigments as well.Back in the day Domestic was all that I recall was around.So we always used that in all recipes.Now its spanish or High Purity for me.Mark

Is High Purity the same as what I see mentioned in recipies as 'Special" ?Will higher purity improve any glaze it is used in, or only if asked for? I know a potter that insists it should always be used instead of the regular less expensive.

I have been using spanish for many years now-before that The domestic was all I ever saw.I also have used High Purity from US Pigments as well.Back in the day Domestic was all that I recall was around.So we always used that in all recipes.Now its spanish or High Purity for me.Mark

Is High Purity the same as what I see mentioned in recipies as 'Special" ?Will higher purity improve any glaze it is used in, or only if asked for? I know a potter that insists it should always be used instead of the regular less expensive.

As always it depends on the glaze. I've been testing RIO, Spanish RIO, Crocus M., and High Purity RIO in various Iron Saturate glazes. So far what I've found is that regular RIO looks a tad better in glazes such as Jen's Juicy Fruit with Iron and Bailey's Red than High Purity RIO. I think that may be simply because the purer the iron is, the stronger it is in a glaze so maybe a tad less High Purity RIO works as well as regular RIO. In some iron saturates High Purity RIO tends to speckle a little more than regular RIO. So far, Crocus M doesn't look good subbed for RIO. Too dark. In some glazes Spanish RIO looks much better than any other form of Iron. It's well worth the time and money to get all 4 (and others such as Yellow Iron and Yellow Ochre) and test test test.

I tried to upload a pic of a test tile that compares regular RIO and High Purity RIO but no matter how small I make the picture I get an error message saying the file it too big!

Using less high purity does do the same thing as as regular red iron-You will discover regular is the best deal for most applications.
If you are using it as a smeared stain on raw clay with no glaze covering then the various kinds look a bit different-Test test test as Johns mantra says.
Mark